1. Field of the Invention
This invention relates to apparatus used in retrieving downhole tools, and more particularly, to a retrieving apparatus requiring only longitudinal motion for engagement to the downhole tool and rotational motion for release of the tool.
2. Description of the Prior Art
Most retrieving devices for downhole tools known in the art require rotational engagement. Typically, a threaded mandrel is threadingly engaged in a sleeve by rotation in one direction. Disengagement requires reverse rotation. Such a reverse rotation is undesirable in that another joint in the tool string may break before the desired disengagement of the overshot and mandrel of the retrieving device. The present invention solves this problem by providing engagement by longitudinal insertion of a threaded mandrel into a threaded, ratcheting C-ring. Longitudinal removal of the mandrel is prevented. A left-hand thread is used, so disengagement is accomplished by normal right-hand rotation. In this way, undesired disengagement of other tool string joints is prevented.
Collet type engaging apparatus are also known, but these are not adapted for supporting the weight of the tool string below the engaging apparatus. Because the ratcheting C-ring of the present invention only allows longitudinal movement of the mandrel in one direction, the full weight of the tool string below the retrieving mechanism may be supported thereby.